RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v9]

[Anton Kozlov]

On Tue, 2 Feb 2021 23:10:17 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   support macos_aarch64 in hsdis
>
> For platform files that were copied from other ports to this port, if the file wasn't
> changed I presume the copyright years are left alone. If the file required changes
> for this port, I expect the year to be updated to 2021. How are you verifying that
> these copyright years are being properly managed on the new files?
> 
> For the new W^X helpers, e.g., WXWriteFromExecSetter, a short comment
> explaining why one was landed in a particular place would help reviewers.
> Also see my comment about creating a new ThreadToNativeWithWXExecFromVM
> helper.
> 
> I'm stopping my review with all the src/hotspot files done for now.

Thank you all for your comments regarding W^X implementation. I've made a change that reduces the footprint of the implementation, also addressing most of the comments. I'll revisit them individually to make sure nothing is forgotten.

The basic principle has not changed: when we execute JVM code (owned by libjvm.so, starting from JVM entry function), we switch to Write state. When we leave JVM to execute generated or JNI code, we switch to Executable state. I would like to highlight that JVM code does not mean the VM state of the java thread. After @stefank's suggestion, I could also drop a few W^X state switches, so now it should be more clear that switches are tied to JVM entry functions.

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PR: https://git.openjdk.java.net/jdk/pull/2200